Metabolism, Toxicokinetics and Hemoglobin Adduct Formation in Rats Following Subacute and Subchronic Acrylamide Dosing

doi:10.1016/S0161-813X(01)00024-9

NeuroToxicology

Volume 22, Issue 3, June 2001, Pages 341-353

https://doi.org/10.1016/S0161-813X(01)00024-9 Get rights and content

Abstract

Long-term, low-dose (subchronic) oral acrylamide (ACR) exposure produces peripheral nerve axon degeneration, whereas irreversible axon injury is not a component of short-term, higher dose (subacute) i.p. intoxication [Toxicol Appl Pharmacol 1998;151:211]. It is possible that this differential axonopathic expression is a product of exposure-dependent differences in ACR biotransformation and/or tissue distribution. Therefore, we determined the toxicokinetics and metabolism of ACR following subchronic oral (2.8 mM in drinking water for 34 days) or subacute i.p. (50 mg/kg per day for 11 days) administration to rats. Both dosing regimens produced moderate levels of behavioral neurotoxicity and, for each, ACR was rapidly absorbed from the site of administration and evenly distributed to tissues. Peak ACR plasma concentrations and tissue levels were directly related to corresponding daily dosing rates (20 or 50 mg/kg per day). During subchronic oral dosing a larger proportion (30%) of plasma ACR was converted to the epoxide metabolite glycidamide (GLY) than was observed following subacute i.p. intoxication (8%). This subchronic effect was not specifically related to changes in enzyme activities involved in GLY formation (cytochrome P450 2E1) or metabolism (epoxide hydrolases). Both ACR and GLY formed hemoglobin adducts during subacute and subchronic dosing, the absolute quantity of which did not change as a function of neurotoxicant exposure. Compared to subacute i.p. exposure, the subchronic schedule produced approximately 30% less ACR adducts but two-fold more GLY adducts. GLY has been considered to be an active ACR metabolite and might mediate axon degeneration during subchronic ACR administration. However, corresponding peak GLY plasma concentrations were relatively low and previous studies have shown that GLY is only a weak neurotoxicant. Our study did not reveal other toxicokinetic idiosyncrasies that might be a basis for subchronic induction of irreversible axon damage. Consequently the mechanism of axon degeneration does not appear to involve route- or rate-dependent differences in metabolism or disposition.

Section snippets

INTRODUCTION

Acrylamide (ACR, 2-propenamide) is a water soluble vinyl monomer which has broad industrial and scientific applications, e.g. water purification, sewage treatment, ore processing, gel electrophoresis (Berger and Schaumburg, 1995, LeQuesne, 1980, Spencer and Schaumburg, 1974a). Early human epidemiological and laboratory animal studies indicated that ACR exposure produced skeletal muscle weakness and ataxia (Spencer and Schaumburg, 1974b, LoPachin and Lehning, 1994). Continued research suggested

Materials

Acrylamide (ACR, 99% pure), S-carboxyethyl-l-cysteine (SCEC), heptane sulfonic acid, chlorzoxazone, acrylonitrile, styrene oxide and styrene glycol were purchased from Sigma/Aldrich Chemical Co. (St. Louis, MO). Dowex 3 and 8N methanolic HCl were purchased from Supelco (Bellefonte, PA). 2,3,3-D₃-acrylamide and 3,3-D₂-cysteine were purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA). 2,3- $^{14} C$ -acrylamide (5.0 mCi/mmol and 1 mCi/ml in ethanol) was purchased from American Radiolabeled

Acrylamide Neurotoxicity

As in previous studies (Lehning et al., 1998, LoPachin et al., 1992), rats exposed to oral or i.p. ACR intoxication developed changes in body weight and classic signs of ACR behavioral neurotoxicity. ACR exposure through drinking water caused a reduction in the rate of body weight gain relative to controls, i.e. ACR-exposed rats gained only 8±13% (mean±S.E.M.) of starting body weight over the 47-day experimental period, whereas age-matched controls rats gained 26±3% over the same time period.

DISCUSSION

We (Lehning et al., 1998, Lehning et al., 2001) and others (Crofton et al., 1996) have reported that subacute ACR intoxication does not cause primary axon degeneration in the CNS or PNS; whereas low-dose, subchronic exposure is associated with abundant fiber loss. The dose rate-dependent differential expression of degeneration suggests that this hallmark morphologic effect (Spencer and Schaumburg, 1974b, Spencer and Schaumburg, 1976) is not a principal neurotoxic event and is instead an

SUMMARY AND CONCLUSIONS

In this study we examined ACR biotransformation and toxicokinetics as a function of subacute i.p. and subchronic oral intoxication. This research was based on the possibility that differential axon degeneration produced by subchronic ACR intoxication (see above) was related to route- or rate-dependent differences in toxicokinetics or metabolism. Our results have confirmed previous findings (Calleman et al., 1990, Bergmark et al., 1991) that the rate of ACR conversion to its epoxide metabolite

Acknowledgements

Research presented in this manuscript was supported by a grant from NIEHS (ES03830-15) to R.M.L. and by the Virginia/Maryland Regional College of Veterinary Medicine. The authors would like to thank Dr. David Dorman, CIIT, Research Triangle Park, NC, for his helpful comments and criticisms.

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^†: Present address: Center for Environmental & Human Toxicology, University of Florida, Building 471, Mowry Road, Gainesville, FL 32611-0885, USA.

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Metabolism, Toxicokinetics and Hemoglobin Adduct Formation in Rats Following Subacute and Subchronic Acrylamide Dosing

Abstract

Section snippets

INTRODUCTION

Materials

Acrylamide Neurotoxicity

DISCUSSION

SUMMARY AND CONCLUSIONS

Acknowledgements

Toxicol. Appl. Pharmacol.

Toxicology

Toxicol. Appl. Pharmacol.

Toxicol. Appl. Pharmacol.

Chem-Biol. Interact.

Biochem. Pharmacol.

Biochem. Pharmacol.

Environ. Toxicol. Pharmacol.

Toxicol. Appl. Pharmacol.

Toxicol. Appl. Pharmacol.

Toxicol. Appl. Pharmacol

Toxicol. Appl. Pharmacol.

Toxicol. Appl. Pharmacol.

Fundam. Appl. Toxicol.

J. Biol. Chem.

J. Chromatogr. Biomed. Appl.

J. Biol. Chem.

Neurotoxicity of glycidamide, an acrylamide metabolite, following intraperitoneal injections in rats

J. Toxicol. Environ. Health

CYP2E1-dependent benzene toxicity: the role of extrahepatic benzene metabolism

Arch. Toxicol.

Acrylamide and glycidamide impair neurite outgrowth in differentiation N1E.115 neuroblastoma without disturbing rapid bi-directional transport of organelles observed by video microscopy

J. Neurochem.

Subchronic toxicity of acrylamide administered to rats in drinking water followed by up to 144 days of recovery

J. Environ. Pathol. Toxicol.